Conventionally, in a communication terminal capable of transmitting and receiving an e-mail (hereinafter, referred to simply as a “mail”), only a limited number of e-mails can be stored in storage units, generally called inbox and outbox (mail boxes), because of a limitation of a memory mounted in the communication terminal. Therefore, if the number of mails in the mail box exceeds a storage limitation (maximum number of mails that can be stored) because of reception or transmission of a new mail, a conventional communication terminal deletes an oldest mail stored, unless a user performs mail protection processing or the like, for example. In addition, in the conventional communication terminal, even a mail with only a small content (hereinafter, referred to as a “short message” for a simple description) such as just “OK”, “Where are you?” or the like, for example, is counted as one mail. Accordingly, if such short messages are exchanged repeatedly, it is easy to reach the maximum number of mails that can be stored in the mail boxes of the conventional communication terminal.
On the other hand, in order to review exchanged mails to check a direction of a conversation, the user needs to read every single mail by opening the inbox and the outbox alternately. Such a reviewing process incur a time-consuming task to the user, especially if the mails comprises a repetition of the short messages as described above, as the user needs to change the mails to view frequently.
As a conventional art capable of handling such a condition, there is disclosed a scheme to secure a memory capacity by deleting or reducing a size of a mail satisfying a predetermined condition such as an old reception date, a less important content or the like, if the number of stored mails reaches the maximum number of mails that can be stored (for example, see Patent Document 1).